fix: token tracking pipeline + premium usage dashboard redesign

Backend fixes:
- Fix totalTokens defaulting to 0 when API omits totalTokenCount (now computes prompt+completion)
- Fix streaming metadata extraction: unwrap response wrapper in Anthropic/Gemini handlers
- Fix Zod schemas: handle SQL SUM(null) with nullable().transform()
- Add is_estimated column migration to token_usage table

Frontend redesign:
- Rewrite Usage page with area charts (nivo/line), horizontal bar model ranking
- StatCard: add trend indicators (% vs previous period) and inline SVG sparklines
- Premium color palette, prompt/completion ratio bar, top models mini-list
- Live indicator with 15s auto-refresh

Design system migration:
- Standardize all components on Gemini Nexus tokens (rounded-xl, border-white/[0.06])
- Refine UI components, proxy tabs, cloud account list, provider groups

package.json

@@ -107,6 +107,7 @@
     "@nestjs/websockets": "^11.1.19",
     "@nivo/bar": "^0.99.0",
     "@nivo/core": "^0.99.0",
+    "@nivo/line": "^0.99.0",
     "@nivo/pie": "^0.99.0",
     "@orpc/client": "^1.13.14",
     "@orpc/server": "^1.13.14",